The present invention generally relates to apparatus and methods for housing electric motors and, more particularly, to apparatus and methods for using low cost light weight motor housing for housing high power density electric motors.
Electric motors with high power density require effective cooling to remove a large amount of heat away from the stator or stator assembly during operation. This requirement is in order to prevent the motor from overheating, which could burn out the motor. Cooling the motor can be accomplished by circulating liquid coolant or cold air through a number of radially constructed fin plates surrounding a stator. While this is necessary, introducing such a design feature significantly increases the cost and weight of a motor.
In a conventional design of a motor housing having a cooling mechanism, the stator support assembly has fin plates which slide into longitudinal slots in the motor housing. In particular, the longitudinal slots are machined into the inner diameter of the motor housing. This machining process is costly because of the complex geometry of the motor housing. Because the slots that need to be machined into the motor housing have sharp corners, great care has to be taken while machining the slots to ensure that mistakes are not made that can predispose the motor housing to cracking at a later time during use. The fact that the exterior of the motor housing is irregular and is not a simple cylinder further increases the difficulty of machining the slots into the motor housing because the machining process typically requires the irregularly shaped motor housing to be positioned perfectly on the machines for milling. The increased difficulty adds to the time and cost of making the motor.
FIG. 1A and FIG. 1B show a high power density electric motor having a conventional motor housing 5, a stator support 7, a rotor assembly 8 and a stator assembly 9. Typically, motor housing for a high power density electric motor has an outer diameter OD of approximately 5 to 9 inches. A “conventional” motor housing is the motor housing that would be utilized without considering the teachings of the present invention. In a conventional motor, for example, although the thickness of the motor housing is typically minimized due to space limitations, for example in an aircraft or other application, the motor housing must be thick enough to receive and securely maintain, without undue stress or cracking, the sharp cornered slots, which are typically square or rectangular, for insertion of the fin plates of the cooling mechanism. As seen from FIG. 1A and FIG. 1B, the motor housing 5 also must have a thick wall in order to accommodate both the depth of the slots and the stress concentration effects at the inner corner of the slots. Since the longitudinal slots 6 in the motor housing have sharp corners, i.e. are rectangular or square, the mechanical stress associated with them is amplified by approximately two to three times at those local areas.
It is therefore useful to have a lower cost design for a high power density electric motor while still allowing for a suitable cooling mechanism to keep such an electric motor from burning out due to its generation of heat. Furthermore, there is a need to reduce the weight of such a motor, especially in the aerospace industry. In addition, there is a need to have a way to reduce the maximum stress in the outer housing derived from the presence of the adjacent cooling mechanism.